Create natural_sort.py (#3286)

* add natural_sort.py

* fix doctest

* add 're' to requirements.txt and fix spelling errors

* delete 're' from requirements.txt

* fixing linting errors

* Update sorts/natural_sort.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update sorts/natural_sort.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update natural_sort.py

Co-authored-by: Christian Clauss <cclauss@me.com>

sorts/natural_sort.py

@@ -0,0 +1,36 @@
+from __future__ import annotations
+
+import re
+
+
+def natural_sort(input_list: list[str]) -> list[str]:
+    """
+    Sort the given list of strings in the way that humans expect.
+
+    The normal Python sort algorithm sorts lexicographically,
+    so you might not get the results that you expect...
+
+    >>> example1 = ['2 ft 7 in', '1 ft 5 in', '10 ft 2 in', '2 ft 11 in', '7 ft 6 in']
+    >>> sorted(example1)
+    ['1 ft 5 in', '10 ft 2 in', '2 ft 11 in', '2 ft 7 in', '7 ft 6 in']
+    >>> # The natural sort algorithm sort based on meaning and not computer code point.
+    >>> natural_sort(example1)
+    ['1 ft 5 in', '2 ft 7 in', '2 ft 11 in', '7 ft 6 in', '10 ft 2 in']
+
+    >>> example2 = ['Elm11', 'Elm12', 'Elm2', 'elm0', 'elm1', 'elm10', 'elm13', 'elm9']
+    >>> sorted(example2)
+    ['Elm11', 'Elm12', 'Elm2', 'elm0', 'elm1', 'elm10', 'elm13', 'elm9']
+    >>> natural_sort(example2)
+    ['elm0', 'elm1', 'Elm2', 'elm9', 'elm10', 'Elm11', 'Elm12', 'elm13']
+    """
+
+    def alphanum_key(key):
+        return [int(s) if s.isdigit() else s.lower() for s in re.split("([0-9]+)", key)]
+
+    return sorted(input_list, key=alphanum_key)
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()